1. Field of the Invention
The present invention relates to a method for the preparation of materials that are useful as stabilizers for organic materials that are prone to deterioration via thermal and/or oxidative mechanisms. More particularly, the present invention relates to a method for the preparation of hindered phenolic antioxidants useful in stabilizing lubricants, especially lubricating oils, or other organic media.
2. Description of Related Art
Prior art methods for the stabilization of polyether polyols and other polymeric materials with antioxidants or other stabilizers and the use of the stabilized polyols in the preparation of polyurethane foams to inhibit scorch are well known. Polyether polyols, used in the manufacture of slabstock flexible and semi-flexible polyurethane foams, are typically stabilized with antioxidant packages comprising phenolic and amine antioxidants which may also contain synergists, such as phenothiazine or various compounds containing phosphite moieties.
WO 94/22945 discloses that organic materials that are subject to thermal and/or oxidative deterioration, e.g., polyether foams and polyurethane foams prepared from polyether polyols, can be stabilized against such deterioration by the addition thereto of a stabilizing amount of a liquid, crystallization-resistant mixture of phenolic esters made up predominantly of phenolic monoester(s), the mixture of phenolic esters being obtained by reacting an alkyl ester of a 3,5-dialkyl-4-hydroxyphenyl alkanoic acid with a polyhydroxyl alcohol under esterification reaction conditions employing an esterification reaction catalyst.
U.S. application Ser. No. 10/014,913, filed Dec. 14, 2001 discloses a method of preparing hindered phenolic antioxidants for lubrication oils or other organic media having reduced tin or titanium levels. A low amount of a tin or titanium catalyst is used resulting in low residual metal levels. The method provides for deactivation of the metal transesterification catalyst with an oxidizing agent, a reducing agent, or clay treatment. Treatment with clay, preferably acid treated clay, and more preferably acid treated bentonite clay, after deactivation with the oxidizing agent or reducing agent can further reduce residual tin levels to less than 10 ppm. By deactivating the metal catalyst prior to isolating the antioxidant from the reaction mixture, further reaction at the terminal diol of the reaction product is prevented. The final product mixture may be used without further purification and has improved solubility in lubrication oils and other organic media.
Oxidative stabilizers similar in structure and utility to the functionalized esters derived from (4-hydroxy-3,5-dialkylphenyl)alkanoic acids are disclosed in U.S. Pat. Nos. 3,644,482; 3,779,945; and 4,032,562. In U.S. Pat. No. 3,644,482, the alkanoic acid esters are terminated with aliphatic hydrocarbons. The compounds of U.S. Pat. No. 3,644,482 are isolated and crystallized.
U.S. Pat. No. 3,779,945 discloses stabilizer compositions containing mixtures of 3-(3,5-dialkyl-4-hydroxyphenyl)propionic acid esters of at least two non-identical alkanediols.
U.S. Pat. No. 4,032,562 discloses phenolic stabilizers, indicated for use in polymers such as polyurethanes, which are obtained by reacting a 3,5-dialkyl-4-hydroxyphenylalkanoic acid, acid chloride, or a lower alkyl ester with a saturated aliphatic glycol under known esterification conditions employing as catalyst a strong acid, such as para-toluene sulfonic acid.
The disclosures of the foregoing are incorporated herein by reference in their entirety.